The folded dipole TV antenna should have an impedance of 300 ohms. Your scanner should have an input impedance of 50 ohms. So, you'd need a 6 to 1 balun.
Most TV baluns transform from 300 ohms to 75 ohms.. But 75 ohms is close enough to 50 ohms so you don't have to worry about it.
The balun should go right at the antenna feedpoint (most are designed to go there). Look at majorco's post above. Note the orange block he refers to.
They come in different shapes and sizes. You can purchase them from eBay
2x Outdoor Antenna 300 To 75 Ohm Coaxial Cable Matching Transformer UHF/VHF/FM | eBay
As zz0468 points out, any chunk of metal will work, but note, if you want the antenna to be optimum, it has to be resonant at the frequency you're receiving. The aluminum loop should be 1.13 meters from tip to tip. (This is the resonant frequency for a dipole at 125 Mhz).